Chapter 27

### INTRODUCTION

The sacroiliac (SI) joint is a common source of chronic low back pain (LBP) with a prevalence rate of 13% to 30%.1, 2, 3, 4, 5, and 6 There is mounting evidence that radiofrequency (RF) neurolysis may provide long-term analgesia in this patient population. Techniques for RF neurolysis using conventional RF electrodes have been reported achieving modest outcomes.7, 8, and 9 More recently, the use of novel cooled RF electrodes for RF neurolysis of the sacroiliac joint provided clinically meaningful efficacy over longer time intervals.10, 11, and 12

Factors leading to a successful outcome following RF neurolysis include adequate diagnosis and accurate electrode placement, which relies on a good understanding of the neuroanatomy.13,14 Accurate electrode placement may be particularly important when treating sacroiliac-mediated pain as the precise innervation of the SI joint has yet to be elucidated. A review of the literature demonstrates that the L5 dorsal ramus and the lateral branches of the S1-S3 are frequently implicated in SI joint pain.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, and 14 The L5 dorsal ramus is reliably accessible at the lateral base of the S1 superior articular pillar (Figure 27-1). It courses along the junction formed between the base of the S1 superior articular process (SAP) and the superior edge of the sacral ala, while the lateral branches of the sacral dorsal roots do maintain an unpredictable distribution across the posterior sacrum.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, and 14

### RELEVANT ANATOMY

• Dissection studies revealed that the upper dorsal portion of the SI joint is primarily innervated by the posterior dorsal ramus of L5, and the lateral branches of S1-S3 (Figures 27-1 and 27-2).

• Complete denervation of these nerves should provide at least partial sacroiliac pain relief in patients whose pain is posteriorly mediated.

• Thus, the L5 dorsal ramus is lesioned as standard practice, in addition to the lateral branches of S1-S3, to denervate the SI joint using cooled RF (Figure 27-3).

###### Figure 27-1.

Anatomical position of dorsal ramus of the L5 nerve root. Maximum neural coagulation is achieved by placing the electrode adjacent and parallel to the course of nerve along the base of the SAP (A and B). The target point for electrode insertion is then identified by rotating the C-arm of the fluoroscope until the lateral edge of the S1 SAP is clearly visible. Once the target point is identified, the electrode is inserted using the “tunnel view.” The trajectory of the electrode is along the sagittal plane to ensure placement of the electrode along the course ...

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